With appearance and spread of machine-to-machine (M2M) communication and a variety of devices such as smartphones and tablet PCs demanding a large amount of data transmission, data throughput needed in a cellular network has rapidly increased. To satisfy such rapidly increasing data throughput, carrier aggregation technology, cognitive radio technology, etc. for efficiently employing more frequency bands and multiple input multiple output (MIMO) technology, multi-base station (BS) cooperation technology, etc. for raising data capacity transmitted on limited frequency resources have developed.
Meanwhile, a communication environment has evolved into increasing density of nodes accessible by a user at the periphery of the nodes. A communication system including high-density nodes may provide a better communication service to the user by cooperation between the nodes. Such a multi-node cooperation communication scheme performing communication with a user equipment (UE) using the same time-frequency resource in plurality of nodes provides much better performance than a conventional communication scheme in which each node operates as an independent BS to perform communication with the UE without mutual cooperation.
As opposed to a conventional centralized antenna system (CAS) (i.e. a single node system) in which antennas are centralized in a BS, a plurality of nodes in a multi-node system is generally separated by a predetermined interval or more. The plurality of nodes may be managed by one or more BSs or BS controllers for controlling operation of each node or scheduling data to be transmitted/received through each node. Each node is connected via a cable or a dedicated line to the BSs or BS controller for managing the node.
Such a multi-node system may be considered a sort of a MIMO system in that distributed nodes may communicate with a single UE or plurality of UEs by simultaneously transmitting/receiving different data streams. Nonetheless, signals are transmitted using nodes distributed at various positions in the multi-node system and thus a transmission region that should be covered by each antenna is reduced relative to antennas included in the conventional CAS. Accordingly, compared with a conventional system implementing MIMO technology in the CAS, transmit power needed when each antenna transmits signals may be reduced in the multi-node system. In addition, since the transmission distance between the antenna and the UE is shortened, path loss is reduced and data can be transmitted at high rate. Then, transmission capacity and power efficiency of a cellular system can increase and communication performance of relatively uniform quality can be achieved irrespective of position of a user in a cell. In the multi-node system, a BS(s) or a BS controller(s) connected to a plurality of nodes cooperatively performs data transmission/reception and therefore signal loss generated in a transmission process is reduced. If nodes separated by a predetermined distance or more cooperatively perform communication with the UE, correlation and interference between antennas is also reduced. Therefore, according to a multi-node cooperative communication scheme, a high signal to interference-plus-noise ratio (SINR) can be obtained.
Due to such advantages of the multi-node system, the multi-node system is used together with or replaces the conventional CAS to emerge as a new base of cellular communication, in order to reduce costs for installing more BSs and maintaining a backhaul network in a next-generation mobile communication system and to improve extend coverage improve SINR.